Consumer and industrial waste management has become one of the most serious and urgent problems of modern life. The severity of the problem is staggering and many proposed solutions are in direct conflict with health and safety standards for the public and with laws and policies protecting the environment. In essence, the problem may be summarized as follows: How does one treat or dispose of human and industrial waste products, natural and synthetic organic materials in the main, without further polluting air, water, and soil; and without creating additional risks and hazards caused by the formation and release of toxic and/or hazardous substances which often are more dangerous to the public than the original waste materials themselves. The problem becomes even more complex and difficult after recognizing the variety of organic material found in waste products; and after appreciating the range of sources of organic materials which contribute to the waste problem overall.
For example, human body waste and food consumption create sewage and water pollution. Industrial manufacturing processes contribute highly toxic, often carcinogenic, organic materials including organic solvents and hazardous by-products from manufacturing operations and chemical compositions used by other businesses and industries as raw materials - many of which are neither biodegradable nor environmentally safe.
The most common solutions to date have been and remain either land disposal or burning of the organic waste material in open-air or closed incinerators. For example, the granular activated carbon (hereinafter "GAC") used as filter material for the purification of potable water and industrial waste water is most commonly regenerated by thermal volatilization in which the organic materials previously adsorbed onto the surface of the GAC are desorbed by volatilization and oxidation at high temperature. This thermal regeneration technique is typically characterized by the loss of GAC due to oxidation and attrition; and by the cost of energy in heating the GAC to temperatures of about 800.degree.-850.degree. C. The thermal volatilization technique has major drawbacks which include: often incomplete destruction of the organic material; the disposal of the incinerated products, if they are not released into the environment at large; the release of toxic products of partial combustion which when volatilized become health hazards for the employees and the public; and the general limitation of being a process dedicated to thermal destruction of the organic material.
Clearly for these reasons, other approaches to in-situ regeneration of GAC as well as to degrading organic materials found in aqueous solutions or suspensions, in organic solvents, and in soil contaminated with gasoline or other organic materials have been investigated.
Current approaches for degrading or destroying organic materials (also termed "mineralizing" by some workers) have, in the main, followed three divergent approaches. The first is application-oriented and seeks practical means for chemical regeneration of exhausted filter adsorption matter, most often exhausted granular activated carbon. These investigations utilize conventional liquid solvents to desorb the organic material retained by the GAC filter and focus primarily on the ability of various solvents, aqueous and organic, to extract organic materials such as substituted benzene and phenol compounds from exhausted GAC [Posey and Kin, J. WPCF 59:47-52 (1987); Martin and Ng, Water Res. 18:59-73 (1984); Martin and Ng, Water Res. 19:1527-1535 (1985); Crittenden et al., Jour. AWWA:74-84 (1987)]. It will be noted and appreciated that the single goal of this general approach is to provide regenerated GAC; there is little or no interest and attention to the question of how to dispose of the liquid solvent after the solvent has desorbed the organic materials and regenerated the adsorbant filter matter.
The second general approach is also application-oriented and is intended primarily for treating domestic water sources for the removal of hazardous natural and/or synthetic organic compounds which are present in relatively low concentration levels, typically 50-500 parts per billion. A constant requirement and characteristic of this approach is the use of an ultraviolet light initiated reaction in combination with a chemical oxidizing agent for the degradation of the hazardous organic compounds in the water. Either ozone gas or hydrogen peroxide is used as the chemical oxidizing agent.
If ozone gas is employed as the oxidizing agent, the gas must be generated where it will be used because ozone is an unstable gas; freshly generated ozone will react in the presence of ultraviolet light with organic compounds to yield a wide diversity of oxidized carbon-containing reaction products, most often peroxides and hydroxyl derivatives of the hazardous organic compounds present initially. In addition, the rate of reaction is often dependent on ultraviolet light intensity. Representative publications describing this technique include William H. Glaze, Environ. Sci. Technol. 21:224-230 (1987); Masten and Butler, Ozone Science and Engineering 8:339-353 (1987); Peyton and Glaze, "Mechanism of Photolytic Ozonation," in Photochemistry of Ennvironmental Aquatic Systems, American Chemical Society, 1987, pages 76-88.
Alternatively, if hydrogen peroxide is employed as the chemical oxidizing agent in combination with ultraviolet light, a variety of smaller molecular weight organic compounds have been degraded partially or completely--if present initially in relatively low concentration. Major differences in the ability to degrade chemically similar compositions have been noted; and complete destruction of hazardous organic materials can occur after reaction with only simple aliphatic compounds. Representative of this technique are the publications of: Sundstrom et al., Hazardous Waste and Hazardous Materials 3:101-110 (1986); Weir et al., Hazardous Waste and Hazardous Materials 4:165-176 (1987); Koubek, E., Ind. Eng. Chem. Proc. Res. Dev. 14:348 (1975); Malaiyandi et al., Water Research 14:1131 (1980); Clarke and Knowles, Effluent and Water Treatment Journal 22:335 (1982).
The third general approach is far more theoretical and research oriented. It focuses upon the photopromoted catalytic degradation of organic material in aqueous suspensions or solutions and in fluid mixtures of water and organic solvents All of these investigations utilize molecular oxygen [O.sub.2 ] as an oxidizing agent in the form of oxygen saturated or aerated water in combination with a solid catalyst, most often a semi-conductor transition element oxide in powder form. This reaction process, often termed "heterogeneous photocatalysis," utilizes a continuously illuminated, photoexcitable solid catalyst to convert reactants adsorbed on the photocatalyst surface. These photocatalysts are semi-conductors which are believed to bring the reactants in the fluid into contact with electrons and/or positive holes which are generated within the solid by photons of energy higher than the band-gap of the solid catalyst [Teichner and Formenti, "Heterogeneous Photocatalysis," Photoelectrochemistry, Photocatalysis, And Photoreactors (M. Schiavello, editor), D. Reidel Publishing Company, 1985, pages 457-489]. These investigations are particularly concerned with purification of drinking water supplies and the aquatic environment; and seek to degrade organic materials such as organo-chlorine compounds in aqueous suspensions or solutions. A representative listing of recent experiments is provided by: Matthews, R. W., Wat. Res. 20:569-578 (1986); Matthews, R. W., J. Catal. 97:565 (1986); Okamoto et al., Bull. Chem. Soc. Jpn. 58:2015-2022 (1985); Pruden and Ollis, Environ. Sci. Technol. 17:628-631 (1983); Ollis et al., J. Catal. 88:89-96 (1984); Ollis, D. F., Environ. Sci. Technol. 19:480-484 (1985); Chang and Savage, Environ. Sci. Technol. 15:201-206 (1981); Tokumaru et al., "Semiconductor-Catalyzed Photoreactions Of Organic Compounds," Organic Phototransformations In Nonhomogeneous Media (Marye Anne Fox, editor), American Chemical Society, Washington, D.C., 1985, pages 43-55; Pelizzetti et al., La Chimica El' Industria 67:623-625 (1985); R. L. Jolley, "Waste Management Trends: The Interface Of Engineering With Chemistry And Toxicological Monitoring," Abstracts of the 193rd National Meeting of the American Chemical Society, Apr. 5-10, 1987. These publications demonstrate and describe the often conflicting and sometimes contradictory state of knowledge and understanding regarding the capabilities and control of photocatalytic oxidation of different organic materials in aqueous suspensions using molecular oxygen as an oxidizing agent. Clearly, there are explicit questions regarding the activity of the metal oxide catalyst employed, for instance between highly active and less active forms of titanium dioxide. In addition, there are continuing discrepancies and contradictions as to whether photocatalytic oxidation using molecular oxygen as an oxidizing agent can provide total degradation of all classes of organic materials with complete conversion to carbon dioxide and other products. There are multiple reports in the literature giving data on the partial oxidation of organic materials without complete degradation into carbon dioxide [Carey et al., Bull. Envir. Contam. Toxic. 16:697-701 (1976); Oliver et al., Envir. Sci. Technol. 13:1075-1077 (1979); Hustert et al., Chemosphere 12:55-58 (1983); Ollis et al., J. Catal. 88:89 (1984)]. There are also other articles stating that some common, organic contaminants in water are completely mineralized in the presence of a titanium dioxide catalyst illuminated with near-ultraviolet light [Barbeni et al., Nouv. J. de Chim. 8:547 (1984); Barbeni et al., Chemosphre 14:195-208 (1985); Matthews, R. W., J. Catal. 97:565 (1986) and Water Res. 20:569-578 (1986)]. Clearly, the current state of knowledge and expectations in this area are in flux and require reconciling a variety of opposing and contrary views.
Despite the existence of these technical and research developments, there has been no attempt to integrate and consolidate these divergent approaches and investigative efforts; nor has there been any recognition or appreciation that a single catalytic process might be suitable for a wide variety of different applications. Moreover, while aqueous suspensions and fluids have been the subjects of multiple investigations and research efforts, there has been comparably little effort expended towards degrading organic materials in organic solvents and fluids--whether for regeneration of solvents or for degradation of organic materials in an environmentally compatible manner. Clearly, therefore, a catalytic process which will completely degrade organic materials generally in a reliable manner in both organic and aqueous fluids would be recognized and appreciated as a major advance and substantive improvement over presently known and available techniques.